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Artificial neural networks (ANNs) have evolved from the 1940s primitive models of brain function to become tools for artificial intelligence. They comprise many units, artificial neurons, interlinked through weighted connections. ANNs are trained to perform tasks through learning rules that modify the connection weights. With these rules being in the focus of research, ANNs have become a branch of machine learning developing independently from neuroscience. Although likely required for the development of truly intelligent machines, the integration of neuroscience into ANNs has remained a neglected proposition. Here, we demonstrate that designing an ANN along biological principles results in drastically improved task performance. As a challenging real-world problem, we choose real-time ocean-wave prediction which is essential for various maritime operations. Motivated by the similarity of ocean waves measured at a single location to sound waves arriving at the eardrum, we redesign an echo state network to resemble the brain's auditory system. This yields a powerful predictive tool which is computationally lean, robust with respect to network parameters, and works efficiently across a wide range of sea states. Our results demonstrate the advantages of integrating neuroscience with machine learning and offer a tool for use in the production of green energy from ocean waves., Comment: 23 pages, 6 figures

Binary kagome compounds TmXn (T = Mn, Fe, Co; X = Sn, Ge; m:n = 3:1, 3:2, 1:1) have garnered recent interest owing to the presence of both topological band crossings and flat bands arising from the geometry of the metal-site kagome lattice. To exploit these electronic features for potential applications in spintronics, the growth of high quality heterostructures is required. Here we report the synthesis of Fe/FeSn and Co/FeSn bilayers on Al2O3 substrates using molecular beam epitaxy to realize heterointerfaces between elemental ferromagnetic metals and antiferromagnetic kagome metals. Structural characterization using high-resolution X-ray diffraction, reflection high-energy electron diffraction, and electron microscopy reveals the FeSn films are flat and epitaxial. Rutherford backscattering spectroscopy was used to confirm the stoichiometric window where the FeSn phase is stabilized, while transport and magnetometry measurements were conducted to verify metallicity and magnetic ordering in the films. Exchange bias was observed, confirming the presence of antiferromagnetic order in the FeSn layers, paving the way for future studies of magnetism in kagome heterostructures and potential integration of these materials into devices., Comment: The following article has been submitted to the Journal of Applied Physics

The main challenge addressed in this paper is to identify individual terms in a superposition of heat kernels on a graph. We establish geometric conditions on the vertices at which these heat kernels are centered and find bounds on the time parameter governing the evolution under the heat semigroup that guarantee a successful recovery. This result can be viewed as a type of deconvolution on a graph., Comment: 7 pages, AMS LaTeX

The high cost of substrates for III-V growth can be cost limiting for technologies that require large semiconductor areas. Thus, being able to separate device layers and reuse the original substrate is highly desirable, but existing techniques to lift off a film from a substrate have substantial drawbacks. This work discusses some of the complexities with the growth of a water-soluble, alkali-halide salt thin film between a III-V substrate and overlayer. Much of the difficulty stems from the growth of GaAs on an actively decomposing NaCl surface at elevated temperatures. Interestingly, the presence of an in-situ electron beam incident on the NaCl surface, prior to and during GaAs deposition, affects the crystallinity and morphology of the III-V overlayer. Here we investigate a wide range of growth temperatures and the timing of the impinging flux of both elemental sources and high energy electrons at different points during the growth. We show that an assortment of morphologies (discrete islands, porous material, and fully dense layers with sharp interfaces) and crystallinity (amorphous, crystalline, and highly textured) occur depending on the specific growth conditions, driven largely by changes in GaAs nucleation which is greatly affected by the presence of the reflection high energy electron diffraction beam., Comment: 18 pages, paper plus supplemental information

Anionic ordering is a promising route to engineer physical properties in functional heteroanionic materials. A central challenge in the study of anion-ordered compounds lies in developing robust synthetic strategies to control anion occupation and in understanding the resultant implications for electronic structure. Here, we show that epitaxial strain induces preferential occupation of F and O on the anion sites in perovskite oxyfluoride SrMnO2.5-dFg films grown on different substrates. Under compressive strain, F tends to take the apical-like sites, which was revealed by F and O K-edge linearly polarized x-ray absorption spectroscopy and density functional theory calculations, resulting in an enhanced c-axis expansion. Under tensile strain, F tends to take the equatorial-like sites, enabling the longer Mn-F bonds to lie within the plane. The anion ordered oxyfluoride films exhibit a significant orbital polarization of the 3d electrons, distinct F-site dependence to their valence band density of states, and an enhanced resistivity when F occupies the apical-like anion site compared to the equatorial-like site. By demonstrating a general strategy for inducing anion-site order in oxyfluoride perovskites, this work lays the foundation for future materials design and synthesis efforts that leverage this greater degree of atomic control to realize new polar or quasi-two-dimensional materials.

Filtered diode array spectrometers are routinely employed to infer the temporal evolution of spectral power from x-ray sources, but uniquely extracting spectral content from a finite set of broad, spectrally overlapping channel spectral sensitivities is decidedly nontrivial in these underdetermined systems. We present the use of genetic algorithms to reconstruct a probabilistic spectral intensity distribution and compare to the traditional approach most commonly found in literature. Unlike many of the previously published models, spectral reconstructions from this approach are neither limited by basis functional forms, nor do they require a priori spectral knowledge. While the original intent of such measurements was to diagnose the temporal evolution of spectral power from quasi-blackbody radiation sources, where the exact details of spectral content was not thought to be crucial, we demonstrate that this new technique can greatly enhance the utility of the diagnostic by providing more physical spectra and improved robustness to hardware configuration for even strongly non-Planckian distributions.

In this his paper, we studied the global dynamics of a two-strain flu model with a single-strain vaccine and general incidence rate. Four equilibrium points were obtained and the global dynamics of the model are completely determined via suitable lyapunov functions. We illustrate our results by some numerical simulations., Comment: 37 pages, 5 figures

In this paper we will consider a mathematical model that describes, the tritrophic interaction between plants, herbivores and their natural enemies, where volatiles organic compounds (VOCs) released by plants play an important role. We show positivity and boundedness of the system solutions, existence of positive equilibrium and its local stability, we analyse global stability of positive equilibrium via the geometrical approach of Li and Muldowney. We pay attention to parameters in order to discuss different types of bifurcations. Finally, we present some numerical simulations to justify our analytical results., Comment: 18 pages, 10 figures, minor corrections, we modify the proof of theorem 3

Web services offer an opportunity to redesign a variety of older systems to exploit the advantages of a flexible, extensible, secure set of standards. In this work we revisit WSEmail, a system proposed over ten years ago to improve email by redesigning it as a family of web services. WSEmail offers an alternative vision of how instant messaging and email services could have evolved, offering security, extensibility, and openness in a distributed environment instead of the hardened walled gardens that today's rich messaging systems have become. WSEmail's architecture, especially its automatic plug-in download feature allows for rich extensions without changing the base protocol or libraries. We demonstrate WSEmail's flexibility using three business use cases: secure channel instant messaging, business workflows with routed forms, and on-demand attachments. Since increased flexibility often mitigates against security and performance, we designed WSEmail with security in mind and formally proved the security of one of its core protocols (on-demand attachments) using the TulaFale and ProVerif automated proof tools. We provide performance measurements for WSEmail functions in a prototype we implemented using .NET. Our experiments show a latency of about a quarter of a second per transaction under load., Comment: 18 pages, 17 figures, followup work to WSEmail: Secure Internet Messaging Based on Web Services in IEEE International Conference on Web Services (ICWS) 2005. Extended version of article to appear in Service Oriented Computing and Applications

Non-collinear, multi-q spin textures can give rise to exotic, topologically protected spin structures such as skyrmions, but the reason for their formation over simple single-q structures is not well understood. While lattice frustration and the Dzyaloshinskii-Moriya interaction are known to produce non-collinear spin textures, the role of electron itinerancy in multi-q formation is much less studied. Here we investigated the non-collinear, helical spin structures in epitaxial films of the perovskite oxides SrFeO3 and CaFeO3 using magnetotransport and resonant soft x-ray magnetic diffraction. Metallic SrFeO3 exhibits features in its magnetoresistance that are consistent with its recently proposed multi-q structure. Additionally, the magnetic Bragg peak of SrFeO3 measured at the Fe L edge resonance energy asymmetrically broadens with decreasing temperature in its multi-q state. In contrast, insulating CaFeO3 has a symmetric scattering peak with an intensity 10x weaker than SrFeO3. Enhanced magnetic scattering at O K edge prepeak energies demonstrates the role of a negative charge transfer energy and the resulting oxygen ligand holes in the magnetic ordering of these ferrates. By measuring magnetic diffraction of CaFeO3/SrFeO3 superlattices with thick CaFeO3 layers, we find that the CaFeO3 helical ordering is coherent across 1 unit cell-thick SrFeO3 layers but not 6 unit cell-thick layers. We conclude that insulating CaFeO3 supports only a simple single-q helical structure in contrast to metallic SrFeO3 that hosts multi-q structures. Our results provide important insight into the role of electron itinerancy in the formation of multi-q spin structures.

The wide variety of complex physical behavior exhibited in transition metal oxides, particularly the perovskites A$B$O$_3$, makes them a material family of interest in many research areas, but the drastically different electronic structures possible in these oxides raises challenges in describing them accurately within density functional theory (DFT) and related methods. Here we evaluate the ability of the ACBN0, a recently developed first-principles approach to computing the Hubbard $U$ correction self-consistently, to describe the structural and electronic properties of the first-row transition metal perovskites with $\left(B=\textrm{V}-\textrm{Ni} \right)$. ACBN0 performs competitively with hybrid functional approaches such as the Heyd-Scuseria-Ernzerhof (HSE) functional even when they are optimized empirically, at a fraction of the computational cost. ACBN0 also describes both the structure and band gap of the oxides more accurately than a conventional Hubbard $U$ correction performed by using $U$ values taken from the literature.

Here we demonstrate a new monoclinic iron oxide phase ({\mu}-Fe$_{2}$O$_{3}$), epitaxially stabilized by growth on (010) {\beta}-Ga$_{2}$O$_{3}$. Density functional theory (DFT) calculations find that the lattice parameters of freestanding {\mu}-Fe$_{2}$O$_{3}$ are within ~1% of those of {\beta}-Ga$_{2}$O$_{3}$ and that its energy of formation is comparable to that of naturally abundant Fe$_{2}$O$_{3}$ polytypes. A superlattice of {\mu}-Fe$_{2}$O$_{3}$/{\beta}-Ga$_{2}$O$_{3}$ is grown by plasma assisted molecular beam epitaxy, with resulting high-resolution x-ray diffraction (XRD) measurements indicating that the {\mu}-Fe$_{2}$O$_{3}$ layers are lattice-matched to the substrate. The measured out-of-plane (b) lattice parameter of 3.12 $\pm$ 0.4 {\AA} is in agreement with the predicted lattice constants and atomic-resolution scanning transmission electron microscopy (STEM) images confirm complete registry of the {\mu}-Fe$_{2}$O$_{3}$ layers with {\beta}-Ga$_{2}$O$_{3}$. Finally, DFT modeling predicts that bulk {\mu}-Fe$_{2}$O$_{3}$ is antiferromagnetic, while the interface region between {\mu}-Fe$_{2}$O$_{3}$ and {\beta}-Ga$_{2}$O$_{3}$ leads to ferromagnetic coupling between interface Fe$^{3+}$ cations selectively occupying tetrahedral positions. Magnetic hysteresis persisting to room temperature is observed via SQUID measurements, consistent with the computationally predicted interface magnetism., Comment: 19 pages and 7 figures

Control of structural couplings at the complex-oxide interfaces is a powerful platform for creating new ultrathin layers with electronic and magnetic properties unattainable in the bulk. However, with the capability to design and control the electronic structure of such buried layers and interfaces at a unit-cell level, a new challenge emerges to be able to probe these engineered emergent phenomena with depth-dependent atomic resolution as well as element- and orbital selectivity. Here, we utilize a combination of core-level and valence-band soft x-ray standing-wave photoemission spectroscopy, in conjunction with scanning transmission electron microscopy, to probe the depth-dependent and single-unit-cell resolved electronic structure of an isovalent manganite superlattice [Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3]x15 wherein the electronic-structural properties are intentionally modulated with depth via engineered oxygen octahedra rotations/tilts and A-site displacements. Our unit-cell resolved measurements reveal significant transformations in the local chemical and electronic valence-band states, which are consistent with the layer-resolved first-principles theoretical calculations, thus opening the door for future depth-resolved studies of a wide variety of hetero-engineered material systems.